Since this essay first appeared, in 1975, much further thought and study have been going on. The likelihood of the “starbow” has been questioned; so has the practicality of the Bussard ramjet. These matters are still controversial, though. Meanwhile, the idea of a matter-antimatter rocket is looking more hopeful than it formerly did. The whole field of interstellar astronautics remains lively, exciting, and infinitely promising.
But mankind will never see that promise fulfilled unless we, today, continue pioneering in those parts of space that we can already reach.